1. Field of the Invention
The present invention relates to a suspension that supports a magnetic head slider, and more particularly relates to a support structure of a microwave signal transmission line on the suspension that is configured to mount a magnetic head for microwave assisted recording.
2. Description of the Related Art
There is a demand for improvement in recording density of magnetic disk devices that are magnetic recording devices. In order to ensure the required signal quality (signal to noise (S/N) ratio) in high density recording, there is a need to reduce the size of magnetic particles that configure a magnetic recording medium in conjunction with the improvement of surface recording density. However, the magnetic particles having reduced size are more likely to cause a magnetization disappearance due to heat fluctuation. In order to prevent this problem and maintain a stable recording state, there is a need to increase magnetic anisotropy energy of the magnetic particles. When a material with high magnetic anisotropy energy is used, coercive force of the recording magnetic recording medium is increased, and therefore, a strong recording magnetic field becomes necessary to record to the magnetic recording medium. Meanwhile, the intensity of magnetic fields generated by a recording head element is restricted by the material and the shape of the recording head element, which makes recording difficult.
In order to resolve this technical problem, energy assisted recording has been proposed in which, at the time of recording, supplemental energy is applied to a magnetic recording medium to lower effective coercive force. A recording system using a microwave magnetic field as a supplemental energy source is called microwave assisted magnetic recording (MAMR). The following references should be referred: J. G. Zhu and X. Zhu, ‘Microwave Assisted Magnetic Recording’, The Magnetic Recording Conference (TMRC) 2007 Paper B6 (2007), and Y. Wang and J. G. Zhu, ‘Media damping constant and performance characteristics in microwave assisted magnetic recording with circular ac field’ JOURNAL of Applied Physics (2009).
In microwave assisted magnetic recording, a system of supplying a microwave magnetic field by a microwave oscillator arranged in a tip end of a magnetic head, and a system of supplying microwave signals (power), the signals being supplied from a microwave signal generation circuit that is independent from the magnetic head, to a microwave generating element are known. The latter is called separate excitation system microwave assisted magnetic recording. With this system, because microwave signals (power) are supplied to a microwave generating element that is formed near a recording head element of a magnetic head slider, there is a need to provide a microwave transmission line onto a head gimbal assembly.
The head gimbal assembly is formed mainly with the magnetic head slider and a suspension. The suspension is formed with a signal transmission line connected to the magnetic head slider, a flexure that supports the magnetic head slider and the signal transmission line, and a load beam that supports the flexure. A configuration in which no load beam is provided is also applicable.
The flexure is needed to secure gimbal function (tracking function of the head above the surface of the magnetic recording medium). In one example, the flexure has a main body part, a support part for the magnetic head slider, and a pair of arm parts that links the main body part and the support part. In order to enhance the gimbal function, it is important to lessen the weight of the signal transmission line mounted on the arm part and the rigidity to enhance deformation performance of the arm part. Therefore, a structure is known in which a separate support part formed of an insulating layer bypassing the outside of the arm part is provided to let the separate support part support the signal transmission line. With this structure, the arm part need not support the signal transmission line, and moreover, an insulating layer for supporting the signal transmission line becomes unnecessary so that reduction in the weight and the rigidity of the arm part is realized.
The above-described configuration can also be applied to the microwave transmission line. Also in this case, the microwave transmission line is supported by the separate support part, so that increase in the weight and the rigidity of the arm part is suppressed due to the same reason. However, with such configuration, a significant impedance mismatch occurs between a line part supported by the separate support part formed of the insulating layer and a line part supported by the flexure, and therefore a significant transmission loss due to the impedance mismatch occurs at the separate support part. A mismatch loss at the separate support part is not a significant problem when recording/reproducing signals with low frequency are transmitted; however, when microwave signals are transmitted, it is too large to ignore.
An object of the present invention is to provide a suspension that can suppress the effects on the gimbal function and that can realize a microwave signal transmission line that can reduce a transmission loss of microwave signals.